The present invention relates to an improved fastening for the housing of a position measuring arrangement, and, in particular, a low-vibration fastening. Position measuring arrangements are used to measure the relative position of two components such as a machine tool or a coordinate measuring machine.
German Patent application no. DE 25 05 587 discloses a length measuring arrangement in which a carrier body is fastened at its ends to one of the components to be measured. The fasteners are articulately constructed. Such a construction allows the carrier body to expand freely via the fasteners relative to the component to be measured when temperature changes occur. The carrier body lies free between the fastening element whereby vibrations are made possible. Such vibrations disadvantageously affect the accuracy of measurement obtainable from a measuring arrangement so constructed.
German Patent application no. DE 35 09 390 A1 discloses a similar measuring arrangement. In addition to the elastic fastening elements at the ends of the housing there are further fastening elements therebetween. Between these fasteners, along the length of the housing, the housing is not in contact with the object to be measured. Thus, vibrations may also be introduced to adversely affect the measuring accuracy of the arrangement.
European Patent application no. EP 0 110 059 B1 discloses a length measuring arrangement with elastic fastening elements at the ends of the housing. Another fastener is located at the middle of the housing to rigidly fasten the housing to the object to be measured. As with the previously described measuring arrangements, the housing is not in contact with the object to be measured between the fasteners.
In a publication entitled "Encapsulated Incremental Length Measuring Systems LS 706, LS 706 C," by Dr. Johannes Heidenhain, June 1993, a length measuring arrangement constructed according to EP 0 110 059 B1 is disclosed. When the housing is attached to the object to be measured, portions of the surface of the housing are in physical contact with the object to be measured. Adhesive friction arises from this contact which hampers the free longitudinal expansion of the housing. Such adhesive friction also introduces measurement inaccuracies.
It is thus desirable to provide a position measuring arrangement wherein the unequal thermal properties of the carrier body and the object to be measured to which the carrier body is fastened, bring about virtually no falsifications or inaccuracies in the resulting measurements. It is also desirable to provide such a measuring arrangement wherein the carrier body is nevertheless relatively securely fastened to the object to be measured so that vibrations are not introduced.